Polymeric separation membranes are typically used in liquid filtration applications requiring high filtration efficiencies of sub-micron particles. Such polymeric separation membranes can be made by suspension deposition. Suspension deposition involves producing a suspension of polymer particles in a solvent; pouring a layer of the suspension; and evaporating the solvent from the poured layer. Such polymeric separation membranes have very small pores, which are suited to efficient separation of submicron, solid particles from fluids. However, polymeric separation membranes are not advantageously used in separations as they are very expensive to produce.
Polymeric filtration media can be produced with melt blowing procedures. Generally, melt blowing produces filtration media having relatively large pores. Therefore, such melt blown polymeric filtration media are too coarse for efficient separation of submicron solid particles from fluids. As a result, such melt blown polymeric filtration media are frequently used in liquid filtration of particles >1 μm.
An alternative process to produce polymeric filtration media is electrospinning. Electrospinning involves applying an electrical charge to a polymer solution or melt. The electrical charge produces electrostatic repulsion, which counteracts the surface tension of the polymer solution or melt. As a result, the polymer stretches into a stream. As the stream dries out in flight, the charge migrates to the surface of stream. Accordingly, the stream thins out until it is deposited as fiber on a grounded collector. Electrospinning produces very fine fibers, which are approximately 0.5 μm or less in diameter. These very fine fibers can provide filtration media with very small pores useful for efficient separation of submicron solid particles from fluids.
However, electro-spun materials are generally not applied in industry. This is due to the fact that electro-spun materials are expensive and are generally not available in commercial quantities.
Thus, there remains a need for a method of making a polymeric filtration medium capable of efficiently separating solid particulates, especially submicron solid particulates, from fluids.